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Science: Tiny tubes prevent liquids from freezing

19 January 1991

If liquids are confined in tiny pores in a glass matrix, they can be
‘supercooled’ to temperatures up to 30 per cent below their normal freezing
temperatures, according to an American researcher. Such ‘geometrically supercooled’
liquids behave very differently from ordinary liquids at low temperature.

DAvid Awschalom of IBM’s Research Center in Yorktown Heights, New York,
has studied a range of liquids trapped in glass, including liquid oxygen,
ethanol, nitrobenzene and carbon disulphide. He presented his results at
a recent meeting of the Materials Research Society in Boston.

Awschalom confined the liquids in pores between 2 and 50 nanometres
across. He found that sound waves travelled through the matrix of liquid-filled
cells in just the same way that they would through a solid. This indicated,
surprisingly, that the liquid behaved like a solid.

Bulk supercooled liquids are unstable, but Awschalom says that a geometrically
supercooled liquid ‘will stay forever below the normal freezing point’.
However, once the liquid does freeze, it forms a normal solid, which does
not melt until it is heated to the normal melting temperature.

Researchers are trying to understand how the geometry of the confining
matrix affects the behaviour of a liquid. Geometric supercooling might allow
scientists to study fluids in states that could not otherwise exist. For
instance, it might be possible to study mixtures of liquids that otherwise
would not mix because there is no temperature at which both are normally
liquids. The technique must lead to the development of new coolants and
lubricants.